[FEATURE]: Plan mode should use a temp file #8725

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Describe the enhancement you want to request

Currently, the agent in plan mode re-prints the whole plan after every suggestion. This is wasting time and tokens. I circumvent that by having it write the plan to a file (but I need to exit Plan mode to do so) and going back and forth with git diffs, but it would be better if the plan was backed by a temp file which I and the agent would edit, showing the diff to the agent when I modify it.